That's fine, but my problem with that line of thinking is that the norms we live with now have evolved to reward the workers who are serving the most affluent g

That's fine, but my problem with that line of thinking is that the norms we live with now have evolved to reward the workers who are serving the most affluent guests, not necessarily those working the hardest or who are paid the least. For example, do you make a point of tipping the cashier at McDonalds? I'd bet that if you tried to and a manager saw you they would refuse it because the company doesn't want others to feel compelled to tip because they want to retain their image of a low-cost restaurant. Coffee shops selling $5 cups of coffee don't have that concern because people who frequent those places probably are a lot less price sensitive than those who eat at fast food restaurants. 15% used to be the norm across the board and adjusted from there based on the level of service. Now 20% is expected regardless of the level of service. In restaurants where a 20% gratuity is included in the bill I've noticed a significant drop-off in the level of service, even to the point where I would tip less than 20% if given the option, and I say that as someone who worked as a waiter at one point.